Roll up, roll up: the Royal Mail could soon be for sale. The postal services bill received a second reading today and Vince Cable, the business secretary, said he hopes to announce the start of the privatisation process in the first half of this parliament. "The government is the wrong shareholder for this company," he said.

OK, but how do you hope to establish a fair price for Royal Mail while running at breakneck speed? The government is trying to do three things at once – remove the company's pension deficit, set a new regulatory regime and introduce private capital.

By contrast, the utility privatisations of the 1980s followed a simpler formula. A regulatory regime was established and refined; companies were given time to adapt and modernise, and only then did privatisation happen. The process took a lot longer than half a parliament.

Of course, the feeling that "something must be done" about Royal Mail is understandable. There have been false starts over the years (notably Labour's abandoned plan to sell a 49% stake) and the sense of crisis around Royal Mail has intensified. But the experience of the 1980s suggests success relies on getting things done in the right order – and sorting out the regulation comes first.

A complication in this case is Royal Mail's pension fund. The government proposes to tow away both the assets of the scheme (£26bn) and the liabilities (£34bn) to allow the company to start from scratch on pensions. In itself, this is sensible: the pensioners get a stronger guarantee, Royal Mail is released from £300m-a-year of top-up payments and an issue that has dominated the company's affairs is resolved.

But what happens if the European commission deems the manoeuvre to be state aid? Disposals, as with Royal Bank of Scotland and Lloyds, would be one remedy. But almost the only slices that could be carved off Royal Mail are GLS and Parcelforce, the two parcels businesses. They are the juiciest pieces in the eyes of the private sector. If either were to go, Royal Mail would be a different company. Its ability to protect a universal postal service, which is one of the twin aims of the bill, would surely be impaired.

The regulatory issue is even more fundamental. It doesn't matter that Ofcom will be taking over from the soon to be abolished Postcomm. The critical point is that the regulator has the ability, to a large degree, to determine Royal Mail's profits. It can set prices, address the "skimming off" of profits by rivals and dictate Royal Mail's freedom to introduce new services. The current "suffocating regulatory approach", as Royal Mail's chief executive, Moya Greene puts it, is the critical issue.

Cable pledges a "level playing field" on regulation. Yes, but let's see it work reliably before trying to put a price tag on Royal Mail. This is a market where today's level pitch can look tilted in no time; letter volumes are forecast to fall 25% to 40% in the next five years.

Against that backdrop, today's £1.3bn of funding for the Post Office – which is to be separated from the Royal Mail and "mutualised" – is welcome. But the absurdity of attempting to value Royal Mail itself in its current form was illustrated by corporate advisory firm Trova Consulting's stab at an answer – £700m to £5.7bn, it said. What a range! The government is attempting to sell an asset where it cannot hope to have a reasonable idea of good value.

Given the risks, would-be buyers (private equity firm CVC, Deutsche Post and Dutch firm TNT are the usual suspects) are likely to bite only if they smell an outright bargain. UK taxpayers risk being short-changed in this rush to privatise. It would be better to fix the regulation before deciding whether to sell.